In recent years, as environment-friendly automobiles, electric automobiles and hybrid automobiles have been developed. Each of the foregoing automobiles has a driving battery in addition to an auxiliary apparatus battery for, as is the case with a conventional automobile, supplying electric power to auxiliary apparatuses. Accordingly, it is required to charge the driving battery and as is the case with a conventional automobile, it is required to charge the auxiliary apparatus battery. In the case where the auxiliary apparatus battery is charged, the electric power of the driving battery is converted into DC electric power by a DC power converter and then the auxiliary apparatus battery is charged with the DC electric power.
Electric power is supplied from the driving battery to the DC power converter by way of a harness; similarly, the auxiliary apparatus battery is charged by way of a harness. In this situation, the electric power supplied from the driving battery needs to cover the electric power that is consumed by the auxiliary apparatuses. Because its voltage is high, the current of the driving battery is approximately 10 A; because insulation is provided in order to prevent an electric shock, shielded wires are utilized. As far as the electric power with which the auxiliary apparatus battery is charged is concerned, the voltage thereof is low, but the current thereof is 100 A or larger; therefore, a thick harness is utilized for the positive side of the output of the DC power converter. Because the electric potential of the negative side of the output is the same as that of the vehicle chassis, the case of the DC power converter, as the negative side, is directly connected with the vehicle chassis through a thick harness, a screw, or the like, as is the case with the positive side.
Meanwhile, in Japanese Patent Application Laid-Open No. H8-320352 (Patent Document 1), an apparatus that detects electric leakage from a driving battery utilized in a DC power converter is disclosed. In the electric leakage detection apparatus disclosed in Patent Document 1 is provided with a high-voltage DC power source that is mounted in a vehicle and is electrically separated from the chassis of the vehicle, two high-resistance protection resistors connected between the positive and negative sides of the high-voltage DC power source, an electric leakage detection resistor whose one terminal is connected with the connection point between the two protection resistors, a switch that opens or closes the connection between the other terminal of the electric leakage detection resistor and the chassis, a voltage measurement unit that measures the voltage across the electric leakage detection resistor, and an electric leakage determination unit that determines electric leakage, based on the output of the voltage measurement unit; the switch opens or closed the connection between the electric leakage detection resistor and the chassis, so that the electric leakage detection apparatus itself intermittently causes a dielectric breakdown.